Just click on the Sell Settings tab for the main course that you're looking to sell, and click on Bundle Additional Courses.
Next, use the drop-down to select courses that you want to bundle alongside the current course and click Update. Now, when a customer purchases the course, they will also gain access to the other courses that you selected.
If you want to sell a Learning Path, you will need to go to the Sell Settings tab of the first course in the Learning Path and use the Bundle Additional Courses button to bundle the Learning Path together with the course.
If you don't have the Bundle Additional Courses button, just let us know at firstname.lastname@example.org.